The present invention relates generally to a bent type zoom optical system, and more particularly to a bent type zoom optical system that is reduced in terms of the whole size and thickness albeit including a reflecting surface in its optical path and having a high zoom ratio as well as an imaging apparatus, information processor and electronic camera apparatus incorporating the same.
In recent years, imaging apparatus using an electronic imaging device as in the case of digital still cameras have been widely available. With the development and widespread use of digital still cameras, there are now growing demands for high image quality and size reductions in general, and for slimmer zoom optical systems having a higher zoom ratio in particular.
As one approach to slimmer optical systems, a mechanism capable of retracting a part of the optical system out of an optical axis during accommodation has been proposed and put to practical use. However, a high image-quality, high zoom-ratio zoom lens grows large in terms of the entire length and the amount of movement in association with zooming, and so size reductions are hard to achieve even with the use of a complicated lens barrel structure.
Now that a collapsible lens mount type lens barrel renders a dust- and water-proof mechanism sophisticated, a bent type zoom optical system favorable for a dust- and water-proof structure provides means advantageous for the enlargement of the area to be taken. For instance, Patent Publications 1, 2 and 3 have proposed a high zoom-ratio optical system incorporating a bent type optical system.
Patent Publication 1
JP-A-8-248318
Patent Publication 2
JP-A-9-138347
Patent Publication 3
JP-A-2004-347712
These prior publications disclose examples having a zoom ratio of as high as 5 or greater; however, they are still less than satisfactory in terms of size reductions, because the optical entire length is long relative to a telephoto-side optical focal length. On the telephoto side, the entrance pupil position remains deep: there is no option but to increase the volume of the first lens group so as to make sure the quantity of rim rays on the telephoto side (specifically, because off-axis light rays on the telephoto side grow high, prism size must be increased so as to make sure the quantity of rim rays), ending up with an increase in the size of the optical system and apparatus.